As shown in a schematic cross-sectional view of FIG. 7, a conventional thermal transfer recording medium 101 used for a thermal transfer printer includes a base sheet 111 and an ink layer 116 disposed on the base sheet 111.
A primer layer 115, whose main component is wax, is disposed between the ink layer 116 and the base sheet 111, and the ink layer 116 is fixed to the base sheet 111 with the primer layer 115 in between.
To execute printing using the thermal transfer recording medium 101, a heating head is pressed to a surface of the thermal transfer recording medium 101 that is the opposite side to the ink layer 116 and the surface of the ink layer 116 is brought in firm contact with a recording sheet.
The heating head is made to conduct electricity and the thermal transfer recording medium 101 is heated by means of thermal conductivity. With this, a heated part of the primer layer 115 is got soft or melts.
When the thermal transfer recording medium 101 and the recording sheet are shifted relatively to the heating head, the ink layer 116 adheres to the recording sheet at a part where the thermal transfer recording medium 101 is separated from the heating head.
In the above state of the thermal transfer recording medium 101 separated from the recording sheet, cohesive failure is caused in the melted primer layer 115, and the above-described heated part of the ink layer 116 is transferred to the recording sheet. In this manner, information on a picture such as characters, figures, etc. is formed on the recording sheet by the collection of transferred ink, and the intended printing is executed.
On the other hand, in order to enhance a preservation property and lustrous property there is a case in which a protective portion formed of transparent resin, namely a protective film, is laminated on the surface of a recording sheet where picture information has been formed, namely on the printing surface.
However, the above-described primer layer 115 having a cohesive failure may stick on the surface of the above-described transferred ink; and since the wax constituting this primer layer 115 and the protective film do not bond together due to lack of sufficient adhesiveness thereof, the protective film and the ink do not stick to each other, so that there may be caused a lift between the protective film and the printing surface to deteriorate the reliability of the protecting function thereof.